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A Pygmy-Owl Challenge

A Pygmy-Owl Challenge

The Northern Pygmy-Owl is a fascinating bird for those of us interested in vocalizations and taxonomy.  Many people think that what we call “Northern Pygmy-Owl” may contain somewhere between two and four species, based on regional differences in vocalizations.  Here’s a brief overview of the differences, according to The Sibley Guide to Birds (2000), with a typical spectrogram and sound of each:

Pacific birds

According to Sibley, birds along the Pacific Coast of North America “give very slow single toots (1 note every 2 or more sec).”  The example below is even slower than most; 2.5 seconds between notes seems pretty standard.  Although one might expect birds in Montana to be part of the Interior West group, the sole recording available seems to fit better in this group.

Interior West group

Very few recordings of this group are available online (or anywhere else) — just two or three from Colorado [1 2] and one from Utah.   They all seem to give single notes at very regular intervals, just over 1 second apart, totalling about 50 “toots” per minute when they’re going full-bore.

Mexican group (“Mountain” Pygmy-Owl)

Sibley says these birds “give mainly paired notes more rapidly (about 1 pair every sec).”  Paired and single notes are usually mixed together, as on the recording below, and the paired notes are only slightly closer together than the single ones:

"Mountain" Pygmy-Owl (Glaucidium gnoma gnoma), Big Bend National Park, TX, 3/28/2008.

However, “Mountain” Pygmy-Owls also sometimes forgo the paired notes in favor of a rapid-fire string of single hoots almost identical to the song of the Northern Saw-whet Owl:

What we don’t know

What exactly is this Northern Pygmy-Owl saying? You could help us find out. Photo taken 11/4/2008 in Mission, BC by NechakoRiver (Creative Commons 2.0)

Nobody knows exactly where the changes between these songtypes occur, or how abrupt they are, because we just don’t have enough data.  Most recordings of Northern Pygmy-Owl are of the highly vocal Mexican birds.  As I mentioned above, very few recordings exist of the Interior West birds.  There are none from potential areas of transition, like Idaho, Wyoming, northern Arizona, or New Mexico.

Now, my friend Arch McCallum is setting out to get to the bottom of this tricky situation — and you can help.

If you have access to Northern Pygmy-owls anywhere in their range this spring and summer, please do one of the following:

  1. Find a singing pygmy-owl.
  2. Get out a stopwatch and count how many “toots” the bird makes in one minute.
  3. Send this information, along with location, date, and time of day, in an email to Arch (mccalluma   AT   appliedbioacoustics.com) or post it in the comments below.

If you wish, you can also make a one-minute audio recording.  (Just take a video with your digital camera, or get a cheap voice recorder if you don’t already have the means.)  Actually, if you wish, you’re welcome to record (or listen to) the bird for longer than a minute!  The more data, the better.

Hope to see a lot of data points roll in this spring!  Here’s to good owling.

Mountain Quail after all?

Mountain Quail after all?

Don Roberson of Creagrus fame sent me an interesting and provocative email in response to the old pygmy-owl vs. chipmunk thread (1 2).  With his permission, I’m reproducing it here for discussion:

A possible word of caution regarding analysis of chipmunk calls as discussed at http://earbirding.com/blog/archives/454:

I don’t necessarily disagree with your conclusions, but there are caveats to be considered. You may have already considered them, but on the off chance you have not, here they are.

1. You rely heavily on Brand (1976) for your starting point, and he studied primarily “Townsend’s Chipmunk” as stated. However, this was prior to the acceptance of the split of “Townsend’s” into four species, as proposed by Sutton & Nadler (1974) and Sutton (1987) [citations below]. Now, the 4-way split is universally accepted.

One of the major reasons for the split was the differences in vocalization between the four species. One of the two papers, probably the 1987 one, goes heavily into differences in calls. It has been a while since I’ve read them, and I don’t recall whether he went into “chips” versus “chuks” but a full background in the vocal differences between the for “Townsend’s” types is important before drawing generalizations from Brand’s 1976 paper. I don’t know how many species of chipmunk Brand reviewed, but there are 25 species in North America.

For more on chipmunk i.d., with some discussion of calls, see my 3-page web set on chipmunk i.d. that starts at
http://creagrus.home.montereybay.com/chipmunks.html
The Townsend’s four-way split and i.d./calls is on page 2 of the set;

2. The call you have posted as probable Merriam’s Chipmunk “chuk” is a very commonly heard vocalization at Chews Ridge. I live in Monterey County and probably know the spot better than any other birder. I have never seen a chipmunk giving the call, although Merriam’s is common there. In fact I have puzzled over what does give the call. I have cautioned many times about claims of pygmy-owl there because of this note. However, I have generally attributed the note to Mt. Quail. In doing Breeding Bird Atlasing there and other similar habitats in the Santa Lucia Mts., there have been circumstances when a Mt. Quail was seen not long after and close to the source of the call.

If it is Merriam’s Chipmunk, that is very interesting, because it can be given in a steady and prolonged series that I haven’t attributed to chipmunks. [On the other hand, ground-squirrels do give a series of steady, prolonged, evenly-paced calls, so it is reasonable that a chipmunk would as well.]

Did any of your correspondents actually see a chipmunk doing these series of steady calls in California? I do think this could be the right answer to the mystery, but I would appreciate some analysis on why it is not a Mt. Quail.

Thanks, Don

Sutton, D. A. 1987. Analysis of Pacific coast Townsend’s Chipmunks (Rodentia: Sciuridae). Southwestern Naturalist 32: 371-376.

Sutton, D. A., and C. F. Nadler. 1974. Systematic revision of three Townsend’s Chipmunks (Eutamias townsendii). Southwestern Naturalist 19: 199-211.

In response to a couple of Don’s questions, I’ll say:

  1. Chipmunks definitely do give long steady series of call notes, both “chips” and “chucks”; the probable Least Chipmunk I recorded in Michigan vocalized at a nearly constant rate for over 12 minutes.  I did visually identify that one as a chipmunk, although didn’t make a visual ID to species.
  2. Some of my correspondents have seen chipmunks making pygmy-owl-like sounds in California, although it’s apparently more common for the source of the sound to be unseen.
  3. I have tracked down the two sources Don cited; if you want PDF copies, email me.  The 1987 paper mentions vocal distinctions only briefly, citing a personal communication from William Gannon and publishing no spectrograms.  Another paper may go into the differences; I haven’t found it yet, but I haven’t searched long either.  Gannon gave a paper at one point — Influence of proximity to rivers on chipmunk vocalization patterns. Gannon, William L. Special Publication the Museum of Southwestern Biology. 1997 24 March; 3:273-285 — but I haven’t had a chance to track it down yet.

I think we may have a lot to learn about chipmunk vocalizations!  Comments?

Pygmy-Owl vs. Chipmunk

Pygmy-Owl vs. Chipmunk

In addition to the comments on my recent pygmy-owl post, I got five private emails, all of which also implicated Merriam’s Chipmunk as the likely source of the pygmy-owl-like sound.  I emailed Doug Von Gausig, and he was very amenable to the possibility that he might have recorded a chipmunk instead of a pygmy-owl.  I think this is likely the case.

The best evidence came from a 1976 paper by Leonard Brand in the journal Animal Behaviour: “The vocal repertoire of chipmunks (Genus Eutamias) in California” (email me for a PDF copy).  In addition to the “chip” calls that are the most common form of alarm note in all ten chipmunk species in California, Brand mentions a “chuck” call that matches our mystery sound:

Chucks were lower pitched than chips, with their fundamental frequency between 0.5 and 2.0 kHz.  Their lowest frequencies were at the beginning and end, with higher frequencies in the middle of the syllable.  Eutamias townsendii chucks had from zero to five harmonics at approximately 2 kHz intervals.  Each chuck was from 0.03 to 0.05 sec long.  Chucks were given by all species, and they all had a form similar to E. townsendii [emphasis mine].  Chucks were usually given…in a steady series, from 50 to 178 per min.

The description is a pretty good match for the pygmy-owl-like sound, but I think the real clincher is Brand’s spectrogram of the “chuck” call:

Townsend's Chipmunk Possible Merriam's Chipmunk
"Chuck" call of Townsend's
Chipmunk (Tamias townsendii),
adapted from Brand (1976), Fig. 5.		Probable "chuck" call of Merriam's
Chipmunk (T. merriami,
Chews Ridge, Monterey County, CA,
1/12/2009. Recording by Andrew
Spencer.

I fiddled with the axes on the spectrogram of Andrew’s recording to make the two as comparable as possible, and although there are slight differences, the similarities are striking, right down to the faint third voice in between the fundamental and the first harmonic.

Brand was using a Kay Electric Company spectrograph machine on the wide-band setting, which explains the much thicker lines on his spectrogram.  Although I’m not a fan of the wide-band setting, I do have to applaud Brand for resisting the temptation to trace his spectrograms, as was the rage in the 1970s.  Thank goodness we have computers to do the dirty work for us these days!

Overall, I see no reason not to identify Andrew’s recording as the “chuck” call of a chipmunk, which would make it a Merriam’s Chipmunk (Tamias merriami), the only species in Monterey County.  Here’s another link to the sound:

I still marvel at the uncanny resemblance to an owl!

Pygmy-Owl Confusion

Pygmy-Owl Confusion

On 12 January 2009, my friend Andrew Spencer recorded an unseen creature on Chews Ridge in Monterey County, California:

Recording by Andrew Spencer
Chews Ridge, Monterey County, CA, 1/12/2009. Recording by Andrew Spencer

To my ear this sounds like a Northern Pygmy-Owl (sensu stricto: Glaucidium gnoma californicum), and the spectrogram shows many of the characteristics of that species.  The note shape is pretty classic, with a sharp initial upslur and terminal downslur, and an overall barely downslurred trend to the rest of the note.  Almost all of the energy is concentrated in the fundamental, but a couple of faint harmonics are visible, which is standard for pygmy-owls.

But a few things about this recording are strange:

  1. The notes are quite short, about half the length of the average Northern Pygmy-Owl note;
  2. The rate of the series is quite fast (on average about 1 note every 0.66 sec), which is more than twice as fast as you’d expect from pygmy-owls from California;
  3. The pitch of the notes is just a little high, about 1.5 kHz, while most Northern Pygmy-Owl notes fall just above 1.0 kHz;
  4. Oddly, Andrew reports that the sound was coming not from a tree or bush, but from somewhere on the ground.  It’s unlikely that Andrew misjudged the origin of the call: he was aiming at it with a parabolic dish, and if the source of the sound hadn’t been close to the focus of the parabola, most likely the harmonic would be absent from the spectrogram and the echo would be louder in relation to the original sound.

Because the sound came from the ground, Andrew surmised that he might have recorded some kind of mammal.  But what kind of mammal could sound so remarkably similar to a pygmy-owl?  If there is a mammal in California that sounds like this, then I want to know about it.

I did manage to find a recording that matched Andrew’s: Doug Von Gausig made this recording in almost the same place: along the Carmel Valley Road just east of Carmel, California, on 24 March 1999.  In an email, Doug told me his pygmy-owl was unseen, but positioned high within the trees in a dense gallery forest.

The bird on Doug’s recording is even higher-pitched and faster than the one on Andrew’s.  Together, these two recordings represent quite a departure from what I’ve come to think of as the “typical” song of californicum.  Xeno-Canto, the Macaulay Library and the Borror Lab, between them, have nine recordings of the primary song of Northern Pygmy-Owl, from California, Oregon, Montana, Colorado and Utah.  None of the birds in these recordings quite match the Spencer/Von Gausig birds in note length or pitch, and most strikingly, none of them come close in rate: the Borror bird from Utah and Jason Beason’s Colorado bird average about one note every 1.5 sec, while the rest, including the Montana bird, average a note every 2.0 sec or more.  At the moment, I’m still a little skeptical that “interior” Northern Pygmy-Owls sing significantly faster than “coastal” Northern Pygmy-Owls on average, but I have long agreed that “Mountain” Pygmy-Owls (Glaucidium gnoma gnoma), which breed from southern Arizona south through Mexico, sing very differently from californicum and probably deserve species status.  Here’s their standard song:

"Mountain" Pygmy-Owl (Glaucidium gnoma gnoma), Big Bend National Park, TX, 3/28/2008.
"Mountain" Pygmy-Owl (Glaucidium gnoma gnoma), Big Bend National Park, TX, 3/28/2008.

In addition to the typical song with the irregular rhythm, “Mountain” Pygmy-Owls apparently sometimes give a faster, stricter song that is very similar to the song of the Northern Saw-Whet Owl (so similar, in fact, that I suspect the two may represent a vastly underrated ID problem).  See the Xeno-Canto forum discussions (here and here) of Allen Chartier’s seven cuts of fast Mountain Pygmy-Owl song from Oaxaca.  I was particularly struck by Rich Hoyer’s understanding of a stepwise slowing trend in pygmy-owl song rates as you move counterclockwise from Mexico to Colorado to California to Baja California Sur.  Up to a point, that jives with the information I have, but what to make of the two birds from Monterey County that sing at a rate of about 80 notes/minute?  Are they representatives of an anomalous local dialect?  Or of a different type of vocalization than the primary song?  Are they not even pygmy-owls at all?

What gives?